I'd like to suggest to anyone running OMV on a raspberry pi for a home nas to use wifi instead of ethernet, as the wifi is on its own interface and therefore you should not have issues sharing bandwidth between the ethernet port and your storage.
Just in case this was non-obvious, I noticed many tutorials online say to connect the RPi via ethernet and really this is a pretty poor idea if you're intending to r/w alot of data from anything other than the root partition.
Cheers